I didn't get as much done on the Messaging chapter as I'd like--virtually nothing, it's mostly just a topics list--but I promised it, so here it is. Also available is the first version of the full book, most of which is of course just placeholders for content to come. But it's nice to see it all in one document, a sneak peek for the future. The book PDF includes the up-to-date versions of the completed chapters (Calendar, Bing Search and Maps) and this first version of Messaging.
More soon: My intention is to get a bit of this done each day whenever possible.